1. Field of the Invention
The present invention relates to a machine tool having a device for effecting the loading and unloading of workpiece set-up pallets between a work table of the machine tool and a pallet support stand disposed in the vicinity of the moving area of the work table.
2. Description of the Prior Art
In known pallet changers, a pair of support stands for slidably supporting pallets are provided on a base installed adjacent a machine tool table. One of the pallets is first unloaded from the table, which is positioned at an unloading station adjacent to one of the support stands, and the other pallet is then loaded onto the table after it has been positioned at a loading station adjacent to the other support stand. One type of the pallet changers is shown and described by Japanese published examined application No. 53-13068, wherein a single transfer device provided on a machine tool slide table performs both the loading and unloading operations. However, the provision of the transfer device on the slide table reduces the space available on the slide table, thereby imposing restraints upon workpieces to be set up on a rotary table which is rotatably mounted on the slide table. In addition, the pallet changer requires a device which, by pivotally moving an engaging member of the transfer device, releases the engaging member from engagement with a work pallet on the rotary table in order that the rotary table carrying the pallet can be rotated on the slide table.
Another type of the pallet changer has been proposed by co-pending U.S. application Ser. No. 289,221 filed on Aug. 3, 1981. This type is provided with first and second transport members, which are guided on a pallet support base installed adjacent a machine tool slide table. The transport members are selectively moved in a direction parallel to first and second pairs of support rails provided on the support base so that a pallet is transferred between an associated one of the first and second pairs of the support rails and the slide table positioned at a loading/unloading station adjacent thereto. The provision of a pair of clutches therein enables a single drive motor to selectively move the first and second transport members. However, there must be provided two sets of mechanisms each for transmitting to an associated one of the transport members driving power that is supplied from the drive motor through an associated one of the clutches.